High voltage current transformer

ABSTRACT

A high voltage current transformer comprising a hollow support insulator within which is arranged a main insulator, a magnetic circuit associated with this, at least one primary winding and at least one secondary winding together with necessary conductors. The main insulator is of tubular form and made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other partially but not completely, with insulator elements of tubular form arranged between them. A first winding (either a primary or a secondary winding) is located around the main insulator and a second winding (either a secondary or a primary winding) is located inside the main insulator approximately opposite to the said first winding. The magnetic circuit comprises two separate core sections, one of which is arranged outside the main insulator and the other one inside it.

United States Patent [1 1 Kalevi Mar. 5, 1974 v 22 Filed:

[ HIGH VOLTAGE CURRENT TRANSFORMER [75] Inventor: Vaino Tuure Kalevi, Panu, Vaasa,

Finland [73] Assignee: 0y Stromberg Ab, Vaasa, Finland Mar. 21, 1973 [21] Appl. No.: 343,457

[30] Foreign Application Priority Data Apr. 7, 1972 Finland 974/72 [52] U.S. Cl 336/69, 336/84, 336/173, 336/178, 336/212 [51] Int. Cl H011 15/04, HO'lf 15/14 58 Field of Search...3 36/69, 79, 84, H178, 17; g 1;, 336/174, 175

839,662 4/1939 France 336/70 Primary Examiner-Thomas J. Kozma Attorney, Agent, or FirmYoung & Thompson [5 7 ABSTRACT A high voltage current transformer comprising a hollow support insulator within which is arranged a main insulator, a magnetic circuit associated with this, at least one primary winding and at least one secondary winding together with necessary conductors. The main insulator is of tubular form and made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other partially but not completely, with insulator elements of tubular form arranged between them. A first winding (either a primary or a secondary winding) is located around the main insulator and a second winding (either a secondary or a primary winding) is located inside the main insulator approximately opposite to the said first winding. The magnetic circuit comprises two separate core sections, one of which is arranged outside the main insulator and the other one inside it.

13 Claims, 2 Drawing Figures 3. 795, 88 1 PATENTED 5 I974 This invention concerns a high voltage current transformer comprising a hollow support insulator within which is arranged a main insulator, a magnetic circuit associated with this, at least one primary winding and at least one secondary winding, together with the necessary conductors. A current transformer can be constructed out of columns which are electrically insulating and at the same time good magnetic conductors in a longitudinal direction, as shown in FIG. 1. The current travelling along the primary conductor 1 induces a magnetomotive force m between the magnet bars 2. The sum of the stray flux 5 thus induced and the secondary flux (1) makes up the primary flux 42,. The longer the bars, the greater is the stray flux. The columns cannot be any shorter than the minimum longitudinal distance over which the voltage U can be safely distributed. For high voltages the columns are so long that it is necessary to have only a small number of primary ampere turns in order to limit the amount of stray flux. This in turn decreases the permissible loading of the transformer and increases its disturbance sensitivity. It is also necessary to use a matching transformer in order to decrease the number of ampere turns.

The purpose of the invention is to eliminate these aforementioned disadvantages.

The transformer in accordance with the invention is mainly characterised in that the main insulator is of tubular form and made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other partially but not completely, with insulator elements of tubular form fitted between them, in that at least one first winding (either a primary or a secondary winding) is located around the main insulator and at least one second winding (either a secondary or a primary winding) is located inside the main insulator at least approximately opposite to the said first winding and in that the magnetic circuit comprises two separate core sections, one of which is arranged outside the main insulator and encloses from outside at least partially said first winding, and the other one is arranged inside the main insulator and enclosures from inside at least partially said second winding.

The invention is described in more detail in the following with reference to the attached drawings of which:.

FlG. l, as previously mentioned, shows a schematic diagram of a conventional high voltage current transformer; and

FIG. 2 shows a cross-section of one embodiment of the current transformer in accordance with the invention.

As shown in FIG. 2, the main insulator is formed by tube 2 whose length is 2H+H, where H z the shortest permissible distance over which the voltage can be distributed in the axial direction of the support insulator, and H is the length of the active parts of the current transformer in the axial direction of the tube. The main insulator tube 2 is made up of cylinders of metal foil 10 oflength H+H located inside each other and thin insulating cylinders 11 of mutually equal thickness and greater length than the foil cylinders, located between the aforementioned metal foil cylinders. At one end of the main insulator tube, the ends of the metal foil cylinders are located at a distance H/m further away from the midpoint of the main insulator tube 2, and correspondingly at the other end, the same distance nearer to the midpoint of the main insulator tube 2 than the end of the next metal foil cylinder inside, where m the number of insulating cylinders 11.

A primary winding cylinder- 4 of length H is wound on the middle part of the main insulator tube coaxially to the tube. A secondary winding cylinder 5 is correspondingly wound, opposite to the primary winding 4 in the axial direction, but, in the radial direction, on the opposite side of the main insulator tube.

The magnetic circuit 3, 6 comprises two separate sections one, 6, of which is located outside the main insulator tube 2 and the other, 3, of which is placed inside it over the distance H. Each of them is at the same potential as that of the winding 4 or 5, located on the same side of the main insulator tube 2 in such a manner that the main insulator tube 2 cuts the magnetic circuit with two air gaps each of the length of the insulating thickness so that windings 4, 5 and that part of the main insulator tube 2 located between them remain within the magnetic circuit 3, 6. The core 3, 6, together with windings 4, 5 and main insulator tube 2 is located within a hollow support insulator 8 in such a way that the axis of the main insulator tube 2 is parallel to the axis of the support insulator 8 and that the end (the lower end) of the main insulator tube 2 where all the ends of the metal foil cylinders 10 are on the outer sur face in completely within the support insulator 8.

The active parts of the transformer and the main insulator tube 2 are thus located completely within the support insulator 8. The section 3 of the core which is at earth potential is in the shape of a reel with flanged ends and it functions as a reel body for the secondary winding 5, being at the same potential as it. The main insulator tube 2, the ends of which extend a distance H at both ends beyond the ends of the core reel 3, is wound over the cylinder of constant cross-section made up of the core reel 3 and the secondary winding 5. As indicated by the dotted lines, the potential is distributed along the longitudinal direction of the main insulator tube 2 inwards at the top part of tube 2 and outwards at the lower end. The primary winding 4 is wound in the form of a cylinder on the main insulator tube 2 opposite to the secondary winding, 5, and the other half of the core 6, which is at the same potential as the primary winding, is located over this.

The effect of the air gap caused by the main insulator tube can be drecreased by increasing the yoke areas.

Differing from the embodiment described above, but within the scope of the invention, the positions of the primary and secondary windings can be interchanged, causing the main insulator tube to be located upsidedown.

What we claim is:

l. A high voltage current transformer, comprising:

a a hollow support insulator;

b a main insulator having tubular form and being arranged within said support insulator and being made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other at least partially, and ofa number of tubular insulator elements arranged between said metal foil tube elements;

c at least one first winding arranged around said main insulator;

d at least one second winding arranged inside said main insulator at least approximately opposite to said first winding;

e a magnetic circuit comprising a first and a second core section, said first core section being arranged around said main insulator and enclosing from outside at least partially said first winding, said second core section being arranged inside said main insulator and enclosing from inside at least partially said second winding; and

f a number of conductors interconnecting the different parts of the transformer.

2. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements are of mutually equal length.

3. A high voltage current transformer as claimed in claim 1, wherein the insulating elements of tubular form are of mutually equal length and are longer than the metal foil tube elements.

4. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements and the insulating elements are of cylindrical shape.

5. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements are in mutually equally spaced steps and the insulating elements are also in mutually equally spaced steps.

6. A high voltage current transformer as claimed in claim 1, wherein the insulating elements are of mutually equal thickness.

7. A high voltage current transformer as claimed in claim 1, wherein the ends of the tube elements overlap only in those parts of the main insulator which are located outside the core in the axial direction of the main insulator.

8. A high voltage current transformer as claimed in claim 1, wherein the first winding and the second winding are in the shape of cylindrical rings located one inside the other.

9. A high voltage current transformer as claimed in claim 1, wherein the inner section of the core is of cylindrical shape and is provided with a groove on which the second winding is wound.

10. A high voltage current transformer as claimed in claim 1, wherein the outer section of the core has the shape of a cylindrical ring and is provided with an inside groove for the first winding.

11. A high voltage current transformer as claimed in claim 1, wherein the axial dimension of the core sections is greater than that of the windings.

12. A high voltage current transformer as claimed in claim 1, wherein the outer section of the core is at the same potential as the first winding.

13. A high voltage current transformer as claimed in claim 1, wherein the inner section of the core is at the same potential as the second winding. 

1. A high voltage current transformer, comprising: a a hollow support insulator; b a main insulator having tubular form and being arranged within said support insulator and being made up of a number of metal foil tube elements located inside each other in such a manner as to overlap each other at least partially, and of a number of Tubular insulator elements arranged between said metal foil tube elements; c at least one first winding arranged around said main insulator; d at least one second winding arranged inside said main insulator at least approximately opposite to said first winding; e a magnetic circuit comprising a first and a second core section, said first core section being arranged around said main insulator and enclosing from outside at least partially said first winding, said second core section being arranged inside said main insulator and enclosing from inside at least partially said second winding; and f a number of conductors interconnecting the different parts of the transformer.
 2. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements are of mutually equal length.
 3. A high voltage current transformer as claimed in claim 1, wherein the insulating elements of tubular form are of mutually equal length and are longer than the metal foil tube elements.
 4. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements and the insulating elements are of cylindrical shape.
 5. A high voltage current transformer as claimed in claim 1, wherein the metal foil tube elements are in mutually equally spaced steps and the insulating elements are also in mutually equally spaced steps.
 6. A high voltage current transformer as claimed in claim 1, wherein the insulating elements are of mutually equal thickness.
 7. A high voltage current transformer as claimed in claim 1, wherein the ends of the tube elements overlap only in those parts of the main insulator which are located outside the core in the axial direction of the main insulator.
 8. A high voltage current transformer as claimed in claim 1, wherein the first winding and the second winding are in the shape of cylindrical rings located one inside the other.
 9. A high voltage current transformer as claimed in claim 1, wherein the inner section of the core is of cylindrical shape and is provided with a groove on which the second winding is wound.
 10. A high voltage current transformer as claimed in claim 1, wherein the outer section of the core has the shape of a cylindrical ring and is provided with an inside groove for the first winding.
 11. A high voltage current transformer as claimed in claim 1, wherein the axial dimension of the core sections is greater than that of the windings.
 12. A high voltage current transformer as claimed in claim 1, wherein the outer section of the core is at the same potential as the first winding.
 13. A high voltage current transformer as claimed in claim 1, wherein the inner section of the core is at the same potential as the second winding. 